How Long Does Metronidazole Stay in Your System? Plus, 7 More Frequently Asked Questions

Metronidazole (Flagyl) is an antibiotic used to treat infections caused by anaerobic bacteria. These bacteria live in places where there is little or no oxygen, such as the mouth, gut, and skin. Metronidazole also treats infections caused by certain parasites. But it can’t be used to treat viral infections, such as the common cold or flu.

Metronidazole is available in oral forms, including tablets, capsules, and suspensions (liquids). It can also be administered topically, vaginally, or by injection. It’s usually taken for 5 to 10 days at a time, but it can be prescribed longer for more serious infections or topical use. Your healthcare provider will decide the best form, dosage, and length of treatment for you, based on your specific situation.

If you’ve been prescribed metronidazole to treat an infection, you may be curious about what to expect. Below, we’ll dive into the answers to eight frequently asked questions about metronidazole.

1. How long does metronidazole stay in your system?

Oral metronidazole usually stays in your system for about 2 to 3 days after your last dose. But the timing can vary from person to person based on several factors.

If you have liver issues, it can take up to 6 days for metronidazole to completely leave your system. This is because metronidazole is broken down more slowly in the body in this case.

If you have specific questions about how your body may process metronidazole, it’s best to reach out to your healthcare provider for advice. They’ll be able to use your medical history to provide you with the most accurate answer.

2. How long does it take metronidazole to work?

Metronidazole begins to work just a few hours after you take it. But it can take a few days before you start to feel better. This is because the medication needs time (several days) to fight infection-causing germs. When used topically for rosacea, it may take 3 to 4 weeks to see noticeable results.

An improvement in symptoms doesn’t mean that an infection is fully cleared, though. That’s why it’s essential to finish the full course of medication that’s prescribed — even if you’re feeling better. If you stop treatment too soon, some bacteria may survive, which opens the door for the infection to come back. It’s also possible for the lingering bacteria to develop antibiotic resistance, making the infection harder to treat in the future.

Metronidazole is typically taken for 5 to 10 days, depending on the infection. Infections in the bones or heart can be more difficult to treat and require longer treatment courses, however. Topical and vaginal regimens may also last for longer periods. Your healthcare provider will make the final call on how long you should take metronidazole.

3. What’s the best time of day to take metronidazole?

There isn’t a specific time of day that’s “best” to take metronidazole. But spreading out oral metronidazole doses evenly throughout the day helps the medication work best. So the best time to take metronidazole really depends on how often you are supposed to take it. Depending on the infection you have, this can range from 2 to 4 times a day.

Here are examples of how your doses can be spread out evenly throughout the day, based on the frequency that’s listed on your prescription:

• Two times daily: Take every 12 hours, such as at 6AM and 6PM.

• Three times daily: Take every 8 hours, such as at 6AM, 2PM, and 10PM.

• Four times daily: Take every 6 hours, such as at 5AM, 11AM, 5PM, and 11PM.

It’s OK if you don’t hit these times exactly, but it helps to get as close as you can. One simple way to help you remember when to take your medication is by pairing your metronidazole doses with activities that are part of your daily routine.

Keep in mind: Topical metronidazole formulations come with their own directions. These forms are often used only once daily. The skin formulation may be applied any time of day, but the vaginal form is generally applied at night.

4. Is oral metronidazole better than other forms of metronidazole?

Oral metronidazole isn’t better than other forms of metronidazole. Which form you’ll use depends on the type of infection you have and how severe it is. Oral metronidazole is effective against most infections, but it may not always be the best option.

For instance, using a topical form of metronidazole may be a better choice for skin and vaginal infections. These forms reduce the amount of medication your body is exposed to, since they’re applied specifically to the infected area. They’re also good options if interactions with oral metronidazole are a concern.

In cases of severe infections requiring hospitalization, injectable metronidazole may be the most effective choice.

5. Does metronidazole treat yeast infections?

No, metronidazole doesn’t treat yeast (fungal) infections. Metronidazole treats infections caused by bacteria or parasites, including bacterial vaginosis and trichomoniasis. Yeast infections are treated with antifungals such as fluconazole (Diflucan) or nystatin (Nystop).

While it’s not common, people taking metronidazole can develop a fungal infection in the mouth and throat called oral thrush. This infection is commonly caused by a yeast called Candida. Symptoms of oral thrush may include:

• White patches in the mouth and throat

• Cotton-like feeling in the mouth

• Loss of taste or metallic taste in mouth

• Cracking and redness at corners of the mouth

If you develop symptoms of oral thrush while taking metronidazole, let your healthcare provider know right away. They may prescribe you an antifungal medication to treat it.

6. Is metronidazole safe to take during pregnancy?

Yes, metronidazole is generally considered safe to take during pregnancy. But there’s ongoing discussion about whether or not it should be used in early pregnancy. Manufacturers caution against its use in the first trimester because of an increased risk of miscarriage. But it’s not clear if this risk is related to metronidazole or the infections it treats.

Studies have found that bacterial vaginosis and trichomoniasis infections can increase the likelihood of having issues during pregnancy, including premature birth and other infections. The CDC recommends that these infections should be treated right away to avoid pregnancy complications.

If you have any concerns about taking metronidazole during your pregnancy, reach out to your healthcare provider. They’ll be able to help you weigh the risks and benefits of taking the medication.

7. What foods or medications should you avoid while taking metronidazole?

It’s important to avoid alcohol while taking metronidazole. Combining metronidazole and alcohol can cause a serious issue known as a disulfiram-like reaction. You should also steer clear of grapefruit and grapefruit juice while taking the medication. When taken together, metronidazole levels in the body can increase, which raises the risk of side effects.

Alcohol and grapefruit aren’t the only things to watch out for. Several medications can also interact with metronidazole, potentially making it less effective or even dangerous. Below is a list of some of the medications that can interact with metronidazole:

• Disulfiram

• Cimetidine (Tagamet HB)

• Warfarin (Coumadin, Jantoven)

• Lithium (Lithobid)

• Seizure medications like phenytoin (Dilantin, Phenytek) and carbamazepine (Tegretol)

• Medications that affect your heartbeat, such as citalopram (Celexa) and levofloxacin

• Antibiotics like clarithromycin and erythromycin

• Antifungals like ketoconazole and fluconazole

To avoid metronidazole interactions, make sure your pharmacist has access to a full list of medications and supplements that you take. They’ll be able to screen for interactions up front.

8. When can you drink alcohol after taking metronidazole?

In general, it’s best to avoid alcohol for at least 3 days after your last dose of metronidazole. Drinking alcohol during and shortly after treatment could lead to a problematic reaction with symptoms that include:

• Nausea

• Vomiting

• Stomach cramps

• Headaches

• Flushing

Making sure that metronidazole is totally out of your system before you drink alcohol helps prevent these uncomfortable symptoms. As always, if you have specific concerns about alcohol and your treatment, give your healthcare provider a call.

How to save on metronidazole

There are ways to save on metronidazole, which is available as both brand-name and generic medications. GoodRx may be able to help you save over 80% off the average retail price of the generic version. Generic oral metronidazole tablets may cost as low as $8.62 at certain pharmacies with a free GoodRx coupon.

What’s more, the generic cream may cost as low as $25.00, while the generic gel may cost as low as $23.00.

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Written by:

Vanessa Carranza, PharmD

Vanessa Carranza, PharmD, is a pharmacist who has dedicated her career to the advancement of medical education for healthcare providers, patients, and caregivers, most notably in the oncology space.

Edited by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

Reviewed by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

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